1. Field of the Invention
The invention relates to a method and a device for determining an extrinsic information.
2. Discussion of the Background
To allow an exact detection of Phase-Shift-Keying (PSK) modulated symbols in a transmission channel of which the phase transmission behavior is time-variable because of phase noise, pilot symbols are transmitted for an estimation of the transmission function of the transmission channel characterizing the time-variable phase-transmission behavior. If a transmission in short blocks is provided and if an estimation of the phase-transmission behavior is required in every block, a coherent detection of this kind impairs the transmission efficiency to a considerable extent and accordingly fails.
In the case of a non-coherent detection of a PSK-modulated symbol, especially a differential PSK-modulated symbol, there is no transmission of pilot symbols. Instead, probability distributions of the phase of the transmission channel are additionally determined in the detection alongside estimated values for the individual transmitted PSK-modulated symbols, which leads to an increase in the complexity of the detection. Barbieri, A. et al. “Soft-Output Decoding of Rotationally Invariant Codes Over Channels with Phase Noise”, IEEE Transactions on Communications, Volume 55, No. 11, November 2007, pages 2125 to 2133, describes a recursive detection method which presents a non-coherent detection of differentially M-PSK-modulated symbols.
This detection method is disadvantageously characterized by a plurality of additions, multiplications and divisions, which impair the detection of PSK modulated symbols in real-time. Moreover, this detection method is characterized by a wide dynamic range of the values to be calculated, which makes a fixed-point implementation more difficult.